This study extends research on proactive behavior at work by examining the extent to which job stressors (time pressure and situational constraints) and affective experiences during the workday are associated with proactive behaviors on the same and the following workday. Results from civil service employees who filled in surveys over 4 consecutive workdays indicated that situational constraints were positively associated with proactive behavior on the same workday. In addition, positive mood was significantly related to proactive behavior on the same and the following workday.